The invention relates to a field effect transistor for high-frequency applications comprising on a semi-insulating monocrystalline substrate a thin active n-doped layer of a material having high electron mobility, on whose surface there is deposited a metallic layer constituting two ohmic contacts which form the source and drain contact regions of the transistor, between which a metallic contact constitutes a gate electrode of the Schottky type.
Such a transistor can be used both as a discrete element and as an element of an integrated circuit and it can be utilized in the high-frequency field.
The invention further relates to a method of manufacturing the transistor.
A transistor as described above is known from the publication of D. Boccon-Gibod in ACTA ELECTRONICA 23, 2, 1980, p. 99-109, entitled "Modele analytique et schema equivalent du transistor a effet de champ en arseniure de gallium".
The transistor described in the aforementioned publication is a MESFET (Metal- Semiconductor field effect transistor) of gallium arsenide (GaAs). A mono-crystalline substrate of semi-insulating gallium arsenide serves as a carrier for a thin layer of n-doped gallium arsenide. There are present on the surface of the n-type layer two ohmic contacts forming the source and the drain, between which a Schottky diode constitutes the gate contact and forms a depleted zone whose thickness essentially depends upon the n-doping of the layer and only slightly upon the metal forming the gate.
Under the gate, a current flows in the direction from drain to source, the value of which current depends upon the physical properties of the n-type layer and upon the geometric form of the conductive channel. The application of a voltage V.sub.GS between the gate and the source modifies the geometry of the channel and especially its thickness and hence the value of the current I.sub.D traversing the transistor for a voltage V.sub.DS between drain and source. The publication of C. Azizi and P. Rossel in ACTA ELECTRONICA 23, 3, 1080, p. 205-221, entitled "Modeles mathematiques due transistor a effet de champ en GaAs pour la conception assistee pour ordinateur des circuits" describes the operation of this transistor and provides an equivalent circuit diagram of it. The drain and source contacts constitute, with the gallium arsenide, contact zones which form resistances in series with the active part of the transistor.
This equivalent circuit diagram shows that it is of great importance to improve the performances of the transistor by reducing these contact resistances. Recent examinations have shown that such a field effect transistor made of a material having a high electron mobility is particularly suitable for use in high-frequency circuits.